The invention concerns a flap disc according to the preamble of claim 1.
The invention concerns an innovation in the structure of a flap disc having a circular backing plate with a peripheral zone and lamellae with pairs of spaced apart opposing longitudinal side edges, the lamellae being arranged about and attached on one side of the backing plate successively around the peripheral zone thereof such that one longitudinal side edge of each lamella overlaps the other longitudinal side edge of the next lamella so as to provide the lamellae in an overlapping roof tiles type configuration on the peripheral zone of the backing plate.
A flap disc is known from DE 35 41 347 in which abrasive lamellae are arranged overlapping like roof tiles around the peripheral zone of a flexible backing pad in the form of a circular disc, whereby said lamellae are inserted through radial slits and firmly clamped on the back by a clamping plate. The backing pad and the clamping plate are in the form of metal discs and are connected along their circumference positively or non-positively. The intention of this arrangement is to enable the flap disc to be transported and used as a one piece tool after manufacture.
DE-GM 88 04 148.4 describes a flap disc which consists of a metal support plate onto which abrasive lamellae are bonded in a fan-type arrangement to form an outer ring. The part of the support plate supporting the abrasive lamellae is bent like a truncated cone. The intention of this is to create a favourable ergonomic shape and increase the strength with respect to centrifugal forces.
DE 38 39 238 describes a flap disc with a backing pad onto which abrasive lamellae are bonded overlapping like roof tiles fan-like on an outer ring. The backing pad is preferably formed as a metal disc containing openings which are preferably round. These holes allow the adhesive to flow through to the back. A depression on the back of the pad enhances the adhesion of the adhesive. At the same time, the pad has several notches in the region of the clamping which guarantee a self-locking effect against loosening of the nut upon clamping tightly. This arrangement is intended to create a backing pad which guarantees high operational reliability and is simple to manufacture.
A flap tool is known from DE 40 20 461 which has a support plate provided with a means of fixing which allows it to be mounted on a drive machine, as well as an abrasive disc comprising a backing in the form of a circular disc detachable from the support plate and an abrasive attached to this. The backing consists of a flexible cloth. The connection between the backing and the support plate is formed by a self-adhesive, detachable, Velcro fastening across the entire area. Abrasive lamellae overlapping like a fan and arranged radially are bonded to the backing. The outside diameter of the backing and the abrasive lamellae attached to it is larger than the outside diameter of a support plate chosen depending on the progressive degree of wear of the abrasive lamellae and with a diameter matched to the respective degree of wear; said support plate is provided with a pin in the centre on the abrasive disc side for a central hole in the backing. Through this arrangement it is intended that as much as possible of the abrasive should be used when grinding in corners.
A flap disc for hand-held grinders is known from DE 195 43 597 which comprises a round backing disc with a central fixing device for attaching it to a hand-held grinder and abrasive lamellae overlapping like a fan fixed to the backing disc and extending to or beyond the outer edge of the backing disc. The surfaces of the abrasive lamellae serve as an abrasive surface. The radial outer narrow sides of the abrasive lamellae form the perimeter of the flap disc. At least the narrow sides of the abrasive lamellae are provided with a curing bonding agent which removes material from the object to be machined and extends to the abrasive surface. This arrangement is intended to create a flap disc which exhibits a long service life even when frequently used in areas like angles, corners or similar not easily accessible places.
With the acknowledged flap discs it is known to use abrasive lamellae having a backing covered with a base bonding coat, thereupon a layer of abrasive grain and on the layer of abrasive grain a first size coat and thenxe2x80x94applied by way of a very elaborate processxe2x80x94a second size coat over the first size coat. The first size coat is intended to ensure the strength of the abrasive grain layer and can also include KBF4, cryolite or similar grinding active fillers. The second size coat contains grinding active fillers important for the abrasive action of the flap disc.
The task of the present invention is to devise a flap disc of the aforementioned type in such a way that the abrasive action is improved but with a reduced demand on materials and production.
This task is solved by the present invention which proposes the use of two different types of lamellae for the lamellae of the flap disc: on the one hand, first lamellae including a backing, a base bonding coat over this, a deposited layer of abrasive grain on the base bonding coat and a size coat over the deposited layer of abrasive grain; and on the other hand, second lamellae including a backing and only one layer of grinding active fillers attached to the backing.
So, for example, every second, third, fourth, etc. lamella can be formed like the first lamella or like the second lamella, and the other lamellae formed like the second lamella or the first lamella. Another possibility is alternating groups of first lamellae and groups of second lamellae, whereby the number of lamellae in the groups may be equal or different.
The arrangement according to the invention has the advantage that the lamellae, on the whole, are simpler and less costly to produce, which in turn makes the flap disc less expensive in the end. By providing the grinding active fillers on separate lamellae with only one bonding layer on the backing, which carries the grinding active fillers, this results in a saving of abrasive grain and it is not necessary to apply the grinding active fillers in a second size coat. Apart from that, there are possibilities for improving the degradation behavior of the grinding active fillers compared to an arrangement in a second size coat according to the state of the art. In doing so, it is also possible to increase the amount of the grinding active fillers which are applied without reducing the cutting ability of the flap disc. At the same time, it has been unexpectedly shown that the abrasive action of the flap disc according to the invention has been improved.